The Share button does not function correctly with Apple Mail: it places the title of the shared page in the body of the email, instead of in the Email Subject field, where every other browser places it.

If I use the Share button in Opera, I need to correct this manually every time, which is annoying. It's better to use the Mailto button extension, which functions correctly. Then you end up with two separate "email page" buttons on the task bar.

But I don't understand why would the Opera developers make it impossible to remove the Share button, or would at least not fix it so it work correctly?

Truth. In Google Chrome, you can cover these unwanted icons extensions - are then available at a convenient menu. In Opera always see colorful trashy icons and additionally the button "share", which also can not hide.